As far as I am aware you cannot have a slash (`/` or `\`) within a filename as they are reserved characters within operating systems.

The principle of URL-encoding (what you referred to as percent-encoding) is the method of using the correct syntax in the URL so that special characters can be sent in the URL without breaking the validity. A better example would have been for filenames that have a space character within them, for example `my file.html` would become `my+file.html` since a valid URL cannot have a space character.

There are not multiple ways URL-encode or decode reserved characters. `%2F` and `%2f` are the same thing, case insensitive, because the _2F_ represents a hexadecimal value, the decimal equivalent of which would be _47_, and if you look at the [ASCII table][1] you'll see that character 47 is the forward slash (`/`). 

`%c0%af` would be in decimal character 192 followed by character 175, both of which are extended ASCII characters and could vary in appearance depending on the font chosen. The HTML equivalent would be `À¯` and might be displayed as À¯, definately not the same as a forward slash as you had thought.


  [1]: http://www.asciitable.com/